Process for production of (meth)acrylic acid with high boiling fraction work-up by means of crystallization

ABSTRACT

A process for production of (meth)acrylic acid is disclosed. The process includes synthesizing and distillatively working-up a crude (meth)acrylic acid phase to obtain a (meth)acrylic acid phase and a dimer phase including (meth)acrylic acid dimers and/or (meth)acrylic acid oligomers. At least a part of the (meth)acrylic acid dimers and/or of the (meth)acrylic acid oligomers from the dimer phase is split to obtain a (meth)acrylic acid including a low-boiling phase and a high-boiling phase including less (meth)acrylic acid than the low-boiling phase. At least a part of the (meth)acrylic acid from the low-boiling phase is separated by forming of one or more crystals to obtain a pure (meth)acrylic acid and a residue. Also disclosed is a device for production of (meth)acrylic acid, a process for production of a polymer as well as chemical products based on or including (meth)acrylic acid or a polymer as well as the use of (meth)acrylic acid or polymers in chemical products.

This application is a national stage application under 35 U.S.C. 371 ofinternational application No. PCT/EP2006/007973 filed 11 Aug. 2006, andclaims priority to German Application No. DE 10 2005 039 156.7 filed 17Aug. 2005, the disclosures of which are expressly incorporated herein byreference.

Aspects of embodiments and embodiments of the present invention relateto a process for production of (meth)acrylic acid, a device forproduction of (meth)acrylic acid, a process for production of a polymeras well as chemical products based on or comprising (meth)acrylic acidor a polymer as well as the use of (meth)acrylic acid or polymers inchemical products.

BACKGROUND

“(Meth)acrylic acid” is used in this text for the compounds with thenomenclature names “methacrylic acid” and/or “acrylic acid”. Of the twocompounds, acrylic acid is the subject of aspects of embodimentsaccording to the present invention.

(Meth)acrylic acid can be produced by various processes. Of particularinterest are processes that start from petrochemical products such aspropylene. In this context, the propylene can be converted on the onehand by catalytic gas phase oxidation or also by vapor phase oxidationwith an oxygen-containing gas such as air, first to acrolein and then toacrylic acid. In this way, in a two-step process, the propylene is firstoxidized catalytically to acrolein, which is then converted to acrylicacid in a second process step, likewise using catalysts. Thethus-obtained acrylic acid is removed from the gaseous reaction mixtureby absorption with water to form an aqueous solution or withhigh-boiling solvents to form a high-boiling solution. The purificationof the acrylic acid then generally occurs by azeotropic distillation ofthe acrylic acid solution, followed by further purification steps. In acomparable way the synthesis of methacrylic acid by catalytic oxidationof isobutylene, t-butanol, methacrolein or isobutyl aldehyde can occurin a gas phase.

Also, there have been attempts to carry out the catalytic reaction insolution rather than in the gas phase. This can occur on the one handwith homogeneous catalysts and on the other hand with heterogeneouscatalysts, such as are known, for example, from DE 102 01 783 A1.Another way of producing acrylic acid starts first with a polyol such asglycerine, which is dehydrated to acrolein, as described in DE 42 38 493C1. The thus-obtained acrolein can then be converted either by gas phaseoxidation or by solution oxidation respectively in the presence ofheterogeneous catalysts or homogeneous catalysts to acrylic acid.

It is common for the (meth)acrylic acid present in the products of thesevarious acrylic acid or methacrylic acid production processes to haveinsufficient purity to be used directly for further processing intopolymers or other subsequent products. In particular in connection withthe production of superabsorbers, which are based substantially uponlightly cross-linked partially neutralized polyacrylic acid and are moreclosely described in F. L. Buchholz and A. T. Graham in “ModernSuperabsorbent Technology”, Wiley-VCH, New York, 1998. In the case ofthe production of superabsorbers, which are mostly used in hygienearticles such as diapers, incontinence products and feminine hygienearticles or medical products such as wound dressings, particularly highdemands are made on the purity of the (meth)acrylic acid. This makes itnecessary for the products of the above described (meth)acrylic acidproduction processes to be subjected to one or more purification steps.In the industrial production of (meth)acrylic acid, these purificationsteps are generally one or more distillations. Although distillation asa purification method is well established on the industrial scale andhas long proven itself, in distillative purification, dimers oroligomers often form because of the heating of the (meth)acrylic acidassociated therewith.

In order to convert these (meth)acrylic acid dimers and/or oligomersinto the respective monomer, the prior art makes a number of suggestions.

Thus, for example, JP Sho 61-36501 B2 describes a thermal splitting ofthe dimeric acrylic acid with a simultaneous distillation of the splitmonomeric acrylic acid. This leads to a separation of a large part ofthe high boiling components, but leaves the concentration of maleicacid, maleic acid anhydride and protoanemonin, which can form at thesame time as impurities in addition to the (meth)acrylic acid dimersand/or oligomers, almost unchanged. The thus-worked-up flow is fed backto the process for production of (meth)acrylic acid and effects anenrichment of protoanemonin, maleic acid and maleic acid anhydride inthe fine purified acrylic acid, which reduces its quality and isparticularly disadvantageous with respect to a further processing ofthis acrylic acid in radical polymerization, since these impuritiesfavor chain breaking reactions and chain transfer reactions in radicalpolymerization.

Furthermore, EP 0 887 334 A1 describes the process for recycling acrylicacid from a composition comprising acrylic acid dimers, acrylic acid,and maleic acid, whereby first the acrylic acid is separated in adistillation device, and the bottom product obtained in thedistillation, which is enriched with the acrylic acid dimers and withthe acrylic acid, is converted in a dimer splitting reactor. Finally,the bottom product obtained in the dimer splitting reactor is conductedback into the distillation device. A reduction of the concentration ofprotoanemonin is not mentioned, although protoanemonin is a hindrance inthe further processing of the acrylic acid. Furthermore, the arrangementdescribed in EP 0 887 334 A1 with a subsequently connected dimersplitting reactor and with partial recycling of the head stream of thedimer splitting reactor into the pre-connected distillation device leadsto an unnecessary increase of the supply flow into the distillationdevice and thereby necessitates a larger size of the distillationdevice.

Aspects of embodiments and embodiments of the present invention relateto at least partially alleviating or to completely overcoming thedisadvantages arising from the state of the art.

Further aspects of embodiments and embodiments of the present inventionrelate to economically working-up the impurities that are present incrude (meth)acrylic acid, such as dimers and/or oligomers and alsomaleic acid, maleic acid anhydride or protoanemonin, during itspurification.

Furthermore, aspects of embodiments and embodiments of the presentinvention relate to achieving a conversion of the (meth)acrylic aciddimers and/or oligomers into (meth)acrylic acid while at the samereducing enrichment of further impurities such as, for example, maleicacid, maleic acid anhydride or protoanemonin.

Further aspects of embodiments and embodiments of the present inventionrelate to providing a device for generation of high purity (meth)acrylicacid, which achieves a purification of impure (meth)acrylic acid tohighest purity with low energy expenditure, with as few operationaldisruptions as possible and more environmentally friendly operation andwith as low a loss as possible of (meth)acrylic acid in the form ofdimeric (meth)acrylic acid or trimeric (meth)acrylic acid or higheroligomers.

In addition, aspects of embodiments and embodiments of the presentinvention relate to a process and a device, whereby the risk ofuncontrolled polymerization of (meth)acrylic acid during the productionand in particular during the purification of (meth)acrylic acid isreduced.

In addition, aspects of embodiments and embodiments of the presentinvention relate to improving, by suitable process improvements anddevice improvements, the production of (meth)acrylic acid in such a waythat the production of chemical products that use polymers of(meth)acrylic acid or that are based upon (meth)acrylic acid isimproved.

Numerous other aspects of embodiments, embodiments, features, andadvantages of the present invention will appear from the description andthe accompanying drawings. In the description and/or the accompanyingdrawings, reference is made to exemplary aspects of embodiments and/orembodiments of the invention, which can be applied individually orcombined in any way with each other. Such aspects of embodiments and/orembodiments do not represent the full scope of the invention. Referenceshould therefore be made to the claims herein for interpreting the fullscope of the invention.

A process according to aspects of embodiments and embodiments of thepresent invention for production (meth)acrylic acid comprises the stepsof:

-   -   a) synthesizing of a crude (meth)acrylic acid phase;    -   b) distillatively working-up the crude (meth)acrylic acid phase        to obtain:        -   a (meth)acrylic acid phase, and        -   a dimer phase comprising (meth)acrylic acid dimers or            (meth)acrylic acid oligomers or (meth)acrylic acid dimers            and (meth)acrylic acid oligomers;    -   c) splitting at least a part of the (meth)acrylic acid dimers or        of the (meth)acrylic acid oligomers or (meth)acrylic acid dimers        and (meth)acrylic acid oligomers from the dimer phase to obtain:        -   a (meth)acrylic acid-comprising low-boiling phase, and        -   a high-boiling phase comprising less (meth)acrylic acid than            the low-boiling phase;    -   d) separating at least a part of the (meth)acrylic acid from the        low-boiling phase by forming of one or more crystals to obtain:        -   a pure (meth)acrylic acid and        -   a residue.

The crude (meth)acrylic acid phase comprises (meth)acrylic acid in oneaspect of an embodiment a range from about 1 to about 80 wt. %, inanother aspect a range from about 5 to about 75 wt. % and in yet anotheraspect a range from about 7 to about 70 wt. %, respectively based on thecrude (meth)acrylic acid phase. The other components of the crude(meth)acrylic acid phase can on the one hand be carriers such assolvents, for example water or aromatics having boiling points higherthan (meth)acrylic acid or carrier gases or at least two of the abovecomponents. Furthermore, the crude (meth)acrylic acid phase oftencomprises impurities such as dimers or oligomers of (meth)acrylic acid,aldehydes, for example acid acetaldehyde, furfural or benzaldehyde,propionic acid, acetic acid, maleic acid, maleic acid anhydride orprotoanemonin. The aldehyde content in one aspect of an embodiment oftenlies in a range from about 100 to about 2,000 ppm and in another aspectin a range from about 200 to about 1,000 ppm. The maleic acid and maleicacid anhydride contents lie in one aspect of an embodiment in a rangefrom about 500 to about 5,000 ppm and in another aspect in a range fromabout 1,000 to about 2,000 ppm. The dimers or oligomers content lie inone aspect of an embodiment in a range from about 0.01 to about 2 wt. %and in another aspect in a range from about 0.2 to about 0.6 wt. %. Theacetic acid content lies in one aspect of an embodiment in a range fromabout 0.2 to about 10 wt. % and in another aspect in a range from about2 to about 4 wt. %. The water content lies in one aspect of anembodiment in a range from about 10 to about 50 wt. % and in anotheraspect in a range from about 30 to about 40 wt. %. The propionic acidcontent lies in one aspect of an embodiment less than about 0.1 wt. %and in another aspect less than about 0.05 wt. %. The protoanemonincontent lies in one aspect of an embodiment in a range from about 10 toabout 1,000 ppm and in another aspect in a range from about 100 to about200 ppm. As noted, the above contents can be applied individually orcombined in any way with each other. The weight amounts (in ppm or inwt. %) are respectively based upon the total weight of the crude(meth)acrylic acid phase.

In aspects of an embodiment relating to a process according to thepresent invention, the synthesis according to step a) is selected fromthe group consisting of (i.) gas phase oxidation, (ii.) dehydration ofan organic molecule comprising at least one OH-group, optionally in oneaspect followed by an oxidation and in another aspect the optionaloxidation comprises gas phase oxidation, (iii.) a liquid phaseoxidation.

The synthesis path of the gas phase oxidation is generally known to askilled person and disclosed, among others, in EP 1 319 648 A1. Fordehydration, in addition to glycerine, a hydroxycarboxylic acid such aslactic acid or β-hydroxypropionic acid are suitable as organic moleculecomprising at least one OH-group.

If glycerine is used as such a molecule, acrolein forms in thedehydration reaction, which can subsequently be subjected to anoxidation, in one aspect either a gas phase oxidation or a liquid phaseoxidation and in another aspect a gas phase oxidation, to obtain acrylicacid. For the case of β-hydroxypropionic acid, acrylic acid is obtaineddirectly by dehydration. Suitable dehydration conditions are known tothe skilled person and can be found, among others, in DE 42 38 493 C1.Routes for liquid phase oxidation for the production of (meth)acrylicacid are also known to the skilled person and can also be found in, forexample, DE 102 01 783 A1.

In further aspects of an embodiment relating to the process according tothe present invention, the distillative work-up according to step b)occurs in at least two distillation steps following each other. To thisend, the mostly liquid crude (meth)acrylic acid phase—generally comingfrom an absorption or quench column—is fed into the first distillationcolumn for carrying out the first distillation step and, after carryingout the first distillation step, the (meth)acrylic acid-richer phase issubjected to a further distillation step. In general, aspects includethe distillative work-up occurring in two, three or four distillationsteps, whereby one aspect includes three distillation steps between theabsorption and/or quench step and the splitting step c). The(meth)acrylic acid phase obtained from the distillative work-up of thecrude (meth)acrylic acid in one aspect comprises at least about 90 wt.%, in another aspect a range from about 92 to about 99.9 wt. % and yetanother aspect a range from about 95 to about 99.8 wt. % (meth)acrylicacid, respectively based upon the (meth)acrylic acid phase. The dimericphase which likewise forms during the distillative work-up of the crude(meth)acrylic acid phase is preferably based upon:

-   (α1) in one aspect about 0.1 to about 75 wt. %, another aspect about    5 to about 70 wt. %, and yet another aspect about 10 to about 65 wt.    % monomeric (meth)acrylic acid;-   (α2) in one aspect about 1 to about 90 wt. %, another aspect about    10 to about 40 wt. %, and yet another aspect about 20 to about 30    wt. % (meth)acrylic acid dimers;-   (α3) in one aspect about 1 to about 25 wt. %, another aspect about 2    to about 20 wt. %, and yet another aspect about 5 to about 15 wt. %    (meth)acrylic acid trimers;-   (α4) in one aspect 0 to about 20 wt. %, another aspect about 1 to    about 10 wt. %, and yet another aspect about 2 to about 8 wt. %    water;-   (α5) in one aspect about 1 to about 92 wt. %, another aspect about    10 to about 75 wt. %, and yet another aspect about 40 to about 57    wt. % oligomers which are larger than (meth)acrylic acid trimers;    and/or-   (α6) in one aspect about 1 to about 20 wt. %, another aspect about 2    to about 15 wt. %, and yet another aspect about 5 to about 10 wt. %    further compounds which are different from the α1-, α2-, α3-, α4-    and α5-compounds, as side products, in particular maleic acid    anhydride,-   whereby the sum of the components (α1) to (α6) is 100 wt. %.

In further aspects of an embodiment relating to the process according tothe present invention, the splitting according to step c) occursthermally. To this end, in one aspect suitable temperatures range fromabout 50 to about 500° C., in another aspect from about 150 to about400° C., and in yet another aspect from about 250 to about 300° C. Ithas further proven advantageous to carry out the splitting in one aspectat a pressure ranging from about 0.1 to about 1,000 bar, in anotheraspect from about 10 to about 800 bar, and in yet another aspect fromabout 80 to about 600 bar. Accordingly, in one aspect relating to aprocess according to the present invention, the splitting according tostep c) occurs at a pressure which is different from about the ambientpressure. The ambient pressure is here the pressure which is found atthe location of the splitting device due to the respective climaticconditions. The residence of the dimer phase during the splitting in asuitable splitting area in one aspect ranges from about 0.1 to about 1hour, in another aspect from about 1 second to about 15 minutes and inyet another aspect from about 1 minute to about 10 minutes.

According to aspects of an embodiment relating to a process according tothe present invention, the splitting occurs in the presence of asplitting agent, which in one aspect comprises water. The water and the(meth)acrylic dimers or (meth)acrylic oligomers are used in a weightratio water: (meth)acrylic acid dimers and/or (meth)acrylic acidoligomers in one aspect ranging from about 0.01:1 to about 10:1, inanother aspect from about 0.1:1 to about 8:1, and in yet another aspectfrom about 0.5:1 to about 6:1.

In particular aspects of an embodiment relating to the process accordingto the present invention, the water is used in one aspect in a molaramount which is at most about 90%, in another aspect at most about 80%,and in yet another aspect at most about 50% of the molar amount of(meth)acrylic acid which is bound in dimeric or oligomeric form (two(meth)acrylic acid molecules in a dimer, three(meth)acrylic acidmolecules in a trimer, etc.).

In further particular aspects of an embodiment relating to the processaccording to the present invention, the water is used in one aspect in amolar amount which is at least about 50%, in another aspect at leastabout 80%, and in yet another aspect at least about 90% of the molaramount of the (meth)acrylic acid, which is bound in dimeric oroligomeric form.

In general, the skilled person will determine the amount of water assplitting agent that is appropriate for splitting simply by suitableprior experiments. Thus the skilled person will continue to add water,at the selected pressure and temperature conditions, until as complete asplitting as possible has occurred and/or until also with furtheraddition of water, no further formation of monomeric (meth)acrylic acidcan be observed.

In aspects of an embodiment relating to the production and working-up ofacrylic acid, the low-boiling phase formed in the splitting comprisesacrylic acid dimers and acrylic acid trimers in one aspect in a totalamount ranging from 0 to about 10 wt. %, in another aspect from about0.1 to about 5 wt. %, and in yet another aspect from about 0.5 to about1 wt. %, respectively, based on the weight of the low-boiling phase.

The high-boiling phase comprises in one aspect at least about 5 wt. %,in another aspect at least about 10 wt. %, and in yet another aspectabout 20 wt. % (meth)acrylic acid less than the low-boiling phase.

In further aspects of an embodiment relating to the process according tothe present invention, at least a part of the low-boiling phase in stepd) is conducted as fluid film over a cold source. In this context, inone aspect the cold source has a surface temperature ranging from about−40 to about 5° C., in another aspect from about −20 to about 0° C., andin yet another aspect from about −10 to about −1° C. The conduction ofthe fluid film over the cold source is in an aspect understood to besuch that the cold source comprises a surface that comes into contactwith the fluid film during its conduction thereover. In a further aspectthe fluid film on the one hand is conducted over the cold source bygravity. In addition, it corresponds to aspects of an embodiment of thepresent invention in which the fluid film is conducted over the coldsource by the action of a pump. In a further aspect it is possible forthe fluid film to be conducted over a cold source both by means ofgravity as well as by pump action. In a particular aspect of anembodiment relating to the process according to the present invention,the fluid film is moved by means of gravity. In yet another particularaspect of an embodiment relating to the process according to the presentinvention, at least a part of the fluid film is present as falling film.

A cold source includes in principal all cold-generating devices, whichappear to the skilled person to be suitable for the aspects ofembodiments of the present invention. Thus, in an aspect the cold sourcecan be present in gaseous form, in which a cold gas flow is blownthrough the fluid film or the fluid film is conducted through a cold gasflow. In, however, another aspect of an embodiment according to thepresent invention, the cold source is designed with a solid surface. Ina further aspect of an embodiment according to the present invention,the cold source is formed at least partially planar. In this way, thefluid film can come into contact with the at least partially formed areaof the cold source to facilitate transfer of the cold of the cold sourceto the fluid film (e.g., heat is removed from the fluid film throughcontact with the at least partially formed area of the cold source).This measure also makes it possible that one or more crystals from atleast one component of the fluid film can form on the surface of thecold source. In one aspect of an embodiment according to the presentinvention, a crystal layer forms in this way at least partially overareas on the surface of the cold source, in turn over which the fluidfilm can flow.

In further aspects of an embodiment relating to the process according tothe present invention, at least a part of the crystals is subjected to asweating. In one aspect, this sweating is generally achieved by slowlyincreasing the temperature of the crystals slightly. In another aspect,this temperature increase occurs slightly above the crystallizationpoint or melting point of the crystals. The crystallization point ormelting point of the crystals is in yet another aspect increased by atleast about 1° C., in still yet another aspect about 2 to about 20° C.,and in yet still yet another aspect by about 1.5 to about 5° C.

In general, during the sweating process, care is taken that the crystalscaused to sweat do not fully melt, but rather at most only to a smallamount. In one aspect, this amount is at most about 20 wt. %, in anotheraspect at most about 10 wt. %, and in yet another aspect at most about 5wt. % of the crystal amount before the start of the sweating.

In further aspects of an embodiment relating to the process according tothe present invention, the crystals are melted after the sweating. Inone aspect, the melting occurs, in comparison to the sweating, at ahigher temperature than the sweating temperature. In another aspect, themelting temperature lies at least about 1° C., in yet another aspect atleast about 5° C., and in still yet another aspect at least about 10° C.above the sweating temperature. The temperature measurements can be madeat the boundary surface between cold source and crystals. In connectionwith the purification of acrylic acid, in one aspect the meltingtemperature ranges from about 15 to about 50° C. and in another aspectfrom about 30 to about 40° C.

In further aspects of an embodiment relating to the process according tothe present invention, the residue from step d) is at least partiallyseparated by a further crystallization in step e) into

-   -   a (meth)acrylic acid-rich phase and    -   an impurity phase.

In the context of the further crystallization, in aspects of embodimentsrelating to the process according to the present invention, the(meth)acrylic acid-rich phase is at least partially conducted into theprocess step d). By this measure, a clear improvement of the inputfactor can be achieved.

The device according to aspects of embodiments relating to the presentinvention for production of (meth)acrylic acid comprises, connected witheach other in a fluid-conducting fashion:

-   α a synthesis area;-   β downstream of the synthesis area, a distillative work-up area,    comprising a bottom zone formed in a lower region of the work-up    area;-   γ downstream of the bottom zone, a heatable pressure container    comprising an upper region and a lower region; and/or-   δ downstream of the upper region, a crystallization area comprising    a first outlet and at least one further outlet.

A fluid conducting fashion means, according to aspects of embodiments ofthe present invention, that the individual device components and/orunits are connected together in such a way that liquids, gases and/orsolids can be transported between individual components and/or units. Inone aspect, this transport between individual components and/or unitsoccurs by means of liquid-conducting pipe work systems or gas-conductingpipe work systems.

A synthesis area is designed, according to the requirements of therespective synthesis parts, to be carried out in a way that is familiarto the skilled person. In one aspect relating to the case of the gasphase oxidation, the synthesis area comprises two reactors connectedwith each other, which comprise a solid state catalyst, which is presenteither as powder or as layer or as a combination thereof, in one aspecton plates or in another aspect in pipes, which in yet another aspect arearranged in bundles. In the case of the dehydration of glycerine, tworeactors connected with each other are likewise present. The first isformed as dehydration reactor in the form of a pressure container. Thesecond reactor for conversion of acrolein to acrylic acid is likewisedesigned, as already described for the gas phase oxidation. For thedehydration of β-hydroxypropionic acid to acrylic acid, only one reactoris necessary.

The distillative work-up area is in one aspect designed as one or moredistillation columns, which is in another aspect connected, particularlyin the case of gas phase oxidation, to a quench and/or absorption area.

The splitting area is also characterized as dimers splitter and is madefrom pressure resistant materials known to the skilled person, such asstainless steel. It is, in particular, designed in such a way that itcan be operated at pressures of at least about 10 bar and temperaturesof at least about 200° C. The splitting area is, additionally, in oneaspect corrosion resistant.

In the context of the crystallization area, in one aspect this comprisesan at least partially planar cooling unit. This cooling unit can consistof one, two or more elements. In another aspect according to anembodiment, the cooling unit is formed from pipes, whereby the productto be cooled flows through these pipes on the inside, and in the outerarea, a cooling agent or heating agent flows around the pipes. Inanother aspect, the planar cooling units are present as plates, whichcan also be arranged in plate series. These plates can in turn comprisehollow spaces. On the one hand, the product to be cooled can flowthrough these hollow spaces. In this case, the plates would be broughtto the respectively suitable temperature by means of a cooling medium orheating medium that passes by the outer surfaces of these plates. Inanother form, the product to be cooled could be conducted past the outersurfaces of the plates, whereby the cooling agent or heating agent flowsthrough the openings in the plates.

In a further aspect according an embodiment relating to the presentinvention, the crystallization area comprises an at least partiallyplanar heating unit. In an additional aspect according to the presentinvention, the crystallization area comprises at least one partiallyplanar cooling unit. In a further aspect according to another embodimentof the present invention, the crystallization area comprises an at leastpartially planar heating/cooling unit. By the provision of aheating/cooling unit in the crystallization area, it is possible tofollow a crystal formation at the heating/cooling unit with a sweatingand melting process. In, therefore, a particular aspect according to thepresent invention relating to the crystallization area, theheating/cooling unit is formed at the same location. This can occur, forexample, by means of a pipe, which accommodates the product to be cooledon its inside and which can be flowed around on the outside either by aheating agent or by a cooling agent. In this way, at one and the samepipe section, both a cooling for crystal formation as well as a heatingprocess for sweating or melting can occur. In a particular aspectrelating to the crystallization areas according to the presentinvention, the installation parts helpful for the operation arecommercially obtainable from the Company Sulzer Chemtech AG,Switzerland.

In a further aspect of an embodiment relating to a device according tothe present invention, the device further comprises

-   ε downstream of the at least one further outlet, a further    crystallization unit.

Any crystallization unit that appears suitable to the skilled person canbe used, including commercially obtainable crystallization units suchas, among others, those from Sulzer Chemtech AG or also those from NiroProcess Technology BV, Netherlands. In an aspect, the crystallizationarea operates dynamically, i.e., continuously, while the crystallizationunit operates statically—also characterized as “batchwise”.

In a further aspect of an embodiment relating to the process accordingto the present invention, a device according aspects of embodiments andembodiments relating to the present invention is used. The processaccording to aspects of an embodiment of the present invention for theproduction of a polymer comprises the steps of:

-   I. producing pure (meth)acrylic acid according to a process    according to aspects of embodiments and/or embodiments the present    invention;-   II. polymerizing of a monomer phase comprising the pure    (meth)acrylic acid to obtain a polymer phase,-   III. working-up of the polymer phase to obtain a polymer.

The polymer according to aspects of an embodiment of the presentinvention is a superabsorber, in this case it is recommended that theacrylic acid monomer is at least partially neutralized with a base, inone aspect sodium hydroxide and that cross-linker is present during thepolymerization. Further details concerning the production of asuperabsorber can also be found, in addition to the above-mentionedreference from Buchholz, in DE 40 20 780 C1. It is, furthermore, notabsolutely necessary for the polymerization process according to aspectsof an embodiment of the present invention to only use the pure(meth)acrylic acid from the process according to aspects of embodimentsand/or embodiments of the present invention. The work-up of the polymerphase can occur by precipitation in a precipitation solvent that doesnot dissolve the polymer formed, by drying or by distillation of thesolvent used in the polymerization according to methods familiar to theskilled person.

Furthermore, aspects of embodiments and/or embodiments of the presentinvention relate to fibers, sheets, formed articles, food or feedadditives, pharmaceuticals, cosmetics, foams, superabsorbers, hygienearticles, paper, leather or textile additives, comprising or based upona (meth)acrylic acid obtainable according to a process according to theinvention or comprising or based on a polymer obtainable according to apolymerization process according to aspects of embodiments and/orembodiments of the present invention.

In addition, aspects of embodiments and/or embodiments of the presentinvention relate to a use of a (meth)acrylic acid obtainable accordingto a process according to aspects of embodiments and/or embodiments ofthe present invention or of a polymer obtainable according to apolymerization process according to aspects of embodiments and/orembodiments of the present invention in or for fibers, sheets, formedarticles, food or feed additives, pharmaceuticals, cosmetics, foams,superabsorber, hygiene articles, paper additives, leather additives ortextile additives.

In this context, the use of the (meth)acrylic acid, in particularacrylic acid, produced according to the process according to aspects ofembodiments and/or embodiments of the present invention, in theproduction of superabsorbing polymers (superabsorbers) is highlighted.In an aspect, superabsorbers are used in hygiene articles such asdiapers, incontinence products and feminine hygiene articles. Here, thesuperabsorber is incorporated according to processes generally known tothe skilled person into absorbent members, also known as cores. Thesecores are, in turn, arranged between a liquid permeable top sheet and agenerally liquid impermeable bottom sheet of the hygiene articles.

Furthermore, aspects of embodiments and/or embodiments of the presentinvention are illustrated by way of example by non-limiting figures.

FIG. 1 shows a schematic representation of the device according toaspects of embodiments and/or embodiments of the invention.

In FIG. 1, a production device 1 comprises a synthesis area 2, whichcomprises, for example in the case of the production of acrylic acid anacrolein reactor 15 for the gas phase oxidation of propene and anacrylic acid reactor 16 for the gas phase oxidation of acrolein. Aquench unit 17 is connected at the acrylic acid reactor 16. The crudeacrylic acid formed therein is transferred from there into a work-uparea 3 with a first column 18 followed by a second column 19. At abottom area 4 in the further column 19 is connected a pressure container5 functioning as “dimer splitter”. Purified acrylic acid (AA) leaves thefurther column 19 via its head. At an upper region 6 of the pressurecontainer 5, a crystallization area 8 is connected. Impurities (HE inFIG. 1) forming during the splitting are discarded from a lower region 7of the pressure container 5. Via a first outlet 9, the purified acrylicacid (AA) obtained in crystallization area 8 is discharged. At a furtheroutlet 10 of the crystallization area 8, a crystallization unit 11 isconnected, out of which impurities (HE) are discarded and an acrylicacid-rich phase is conducted back to the crystallization area 8. Thecrystallization area 8 comprises a cooling unit 12, a heating unit 13and a heating/cooling unit 14, over which a falling film 20 isconducted, out of which crystals 21 can form by cooling, which are firstcaused to sweat by heating and can than be melted.

LIST OF REFERENCE NUMERALS

-   1 production device-   2 synthesis area-   3 work-up area-   4 bottom area-   5 pressure container-   6 upper region-   7 lower region-   8 crystallization area-   9 first outlet-   10 further outlet-   11 crystallization unit-   12 cooling unit-   13 heating unit-   14 heating/cooling unit-   15 acrolein reactor-   16 acrylic acid reactor-   17 quench unit-   18 first column-   19 further column-   20 falling film-   21 crystal

1. A process for production of (meth)acrylic acid, comprising the stepsof: a) synthesizing a crude (meth)acrylic acid phase wherein crude(meth)acrylic acid comprises from about 1 to about 80 wt % of(meth)acrylic acid; wherein said synthesizing a crude (meth)acrylic acidphase is selected from the group consisting of gas phase oxidation,dehydration of an organic molecule having at least one OH-group whereinthe organic molecule is selected from the group consisting of glycerine,lactic acid and β-hydroxypropionic acid, optionally followed by anoxidation, and liquid phase oxidation b) distillatively working-up thecrude (meth)acrylic acid phase to obtain: a (meth)acrylic acid phase,and a dimer phase comprising (meth)acrylic acid dimers or (meth)acrylicacid oligomers or both; c) splitting at least a part of the(meth)acrylic acid dimers or of the (meth)acrylic acid oligomers or bothfrom the dimer phase to obtain: a (meth)acrylic acid-comprising a lowboiling phase, and a high boiling phase comprising less (meth)acrylicacid than the low boiling phase; wherein said high boiling phase isdiscarded; d) separating at least a part of the (meth)acrylic acid fromthe low boiling phase by forming one or more crystals to obtain: a pure(meth)acrylic acid, and a residue.
 2. A process according to claim 1,wherein at least a part of the low boiler phase in step d) is providedas fluid film over a cold source.
 3. A process according to claim 2,wherein at least a part of the fluid film comprises a falling film.
 4. Aprocess according to claim 2, wherein the cold source comprises an atleast partially planar form.
 5. A process according to claim 1, whereinat least a part of the crystals are subjected to a sweating.
 6. Aprocess according to claim 5, wherein the crystals are melted after thesweating.
 7. A process according to claim 1, wherein the distillativework-up according to step b) occurs in at least two distillation stepsfollowing each other.
 8. A process according to claim 1, wherein thesplitting according to step c) occurs thermally.
 9. A process accordingto claim 8, wherein the splitting according to step c) occurs under apressure which is different from the ambient pressure.
 10. A processaccording to claim 1, further comprising the step of e) crystallizingthe residue of step d) into a (meth)acrylic acid-rich phase, and animpurity phase.
 11. A process according to claim 10, wherein the(meth)acrylic acid-rich phase is at least partially supplied to processstep d).